14 DARWINISM AND HUMAN LIFE 



(III) VARIABILITY OF LIVING CREATURES. What 

 do we owe to Darwin ? A vivid presentation of 

 the idea of variability, or organic flux. There had 

 been, of course, transformists before his day, but 

 either they had not the idea very clearly in their 

 own minds or they failed in making it convincing 

 to others. So it was that Darwin had to make 

 way against the general conviction of contemporary 

 naturalists that species were fixed. In 1844 he 

 wrote to Hooker : " I am almost convinced . . . 

 that species are not (it is like confessing a murder) 

 immutable." The idea seems to have suggested 

 itself more than once on the Beagle voyage ; for 

 instance, when he found fossils in Argentina very 

 like living forms and yet different. 



In forming his impression of the variability of 

 living creatures Darwin depended on what has 

 taken place in domestication and cultivation, 

 on the experience gained in his systematic work 

 that specific characters are far from being constant, 

 and that so-called varieties often link species to 

 species. A species is a group of similar individuals 

 of common descent, capable of pairing together, 

 and breeding more or less true. It may be repre- 

 sented by a constellation of dots, densest towards 

 the centre (which means that the great majority 

 are very like one another) and thinning out to- 

 wards the periphery where the variants extend 

 as outliers in different directions. When we 

 begin to study a corner of the zoological sky it 

 seems to be covered with very distinct constella- 

 tions, and it is all clear ; but in many cases deeper 

 study shows that one constellation is connected 

 with another by outliers, and that there is con- 

 tinual flux. 



